The present invention broadly relates to a flat roof comprising a substructure, panel-shaped elements which are laid loosely on the substructure, and corrugated cover members positioned on the panel-shaped elements.
According to the general definition, the term "flat roof" designates roofs having a maximum slope of about 20 degrees with reference to a horizontal plane.
The surface of a flat or slightly sloped roof, i.e. more generally of a "flat roof", belong to those roofs having surfaces on which the flow of air, i.e., wind, can produce the greatest vacuum or sub-atmospheric pressure. The absorption and deflection of the wind force, which acts upon the flat roof due to the creation of a vacuum and which force is directed to a lift-off of the roof structure becomes more difficult the lighter the weight of the roof structure.
In the case of a flat roof having a light weight substructure, or in the case of an old flat roof, an improvement in the thermal insulation oftentimes is highly desirable if not required. For such a roof, an additional layer of thermal insulating material can be applied. The thermal insulating material layer generally consists of individual panels of a suitable thermal insulating material. Depending on the substructure, the individual panels can be mechanically secured to the substructure of the roof, albeit in a labor-consuming manner.
However, the possiblity of a mechanical attachment to the above described type of flat roof is excluded for a so-called "upside-down roof" which has a moisture and vapor resistant barrier membrane placed below the layer of thermal insulating panels. Such an upside-down roof has the great advantage that the thermal insulation layer simultaneously serves as protection for the barrier membrane which ordinarily consists of a relatively fragile sheet or film, for example of a synthetic resinous material. The thermal insulation panels are coated with a cementitious material or mortar, or are covered by a layer of gravel, concrete blocks or panels on their upper surfaces to protect them from UV-radiation. Lapped joints may be provided between the individual insulation panels to allow some pressure compensation between the upper and lower sides of the panels. This pressure compensation is better, the more similar the external distribution of pressure on the roof surface becomes to a linear distribution. At a constant external distribution of pressure, during gusts of wind, equalization of pressure is practically complete such that the resulting wind gust loading of the insulation panels is nearly zero. However, in areas adjacent to or near the outer perimeter of the roof this external pressure distribution is not linear. In these peripheral areas, the large resulting wind loads inevitably cause a lift-off of lightweight insulation panels if they are not reliably secured to the substructure of the roof by locking or securing members or by a frictional connection. In principle, the problem could be solved by application of an additional load, for example by an increase in the amount of gravel or by application of a layer of concrete of sufficient increased thickness on the insulation panels. However, such an additional load is not possible for roofs of light construction or for roofs the carrying capacity of which is already at its limit, e.g. for an old roof construction which is in need of retrofitting with an upside-down roof. Furthermore, the retention of gravel in the critical areas of the roof is not always assured due to movement of the gravel caused by wind and rain.